Method of producing alloy steel



Sept. 29, 1964 o. w. REEN 3,150,444

- METHOD OF PRODUCING ALLOY STEEL A Filed April 26, 1962 FIG. 2

United States Patent 3,150,444 METHOD OF PRODUCING ALLOY STEEL Orville W. Reen, Natrona Heights, Pa., assignor to Allegheny Ludlum Steel Corporation, Brackenridge, Pa., a corporation of Pennsylvania Filed Apr. 26, 1962, Ser. No. 199,475 6 Claims. (Cl. 29-420.5)

This invention relates to a new method of obtaining heat hardenable steel and relates in particular to a method of obtaining heat hardenable' alloy steel with a preferred structure and which exhibits maximum response to heat treatment. The present invention is particularly useful and desirable in producing high alloy steels susceptible to hardening in response to quenching from elevated temperatures, such as high speed tool steels.

Steel alloys that are susc'eptibleto hardening by quenching from an elevated temperature exhibit an annealed structure that consists essentially of spheroidized carbides in a matrix of ferrite. The carbides themselves are a phase composed of a combination of iron and carbon or, in the case of many alloys, a complex of alloying metals plus iron and carbon. The phenomenon of hardening is dependent on the transformation of gamma iron or austenite (which is the structural phase of steel as heated to above its phase transformation temperatures), to martensite, which is a hard, strong, transformation product of austenite which hasbeen cooled sufficiently rapidly to avoid other possible transformation products. Carbon is a necessary element in the formation of gamma iron or austenite and the quantity of carbon present in the austenite has a direct effect on the formation of martensite upon quenching or quenching and tempering. The annealed steel will exhibit carbide in a matrix of ferrite since ferritewill retain only a limited amount of carbon in solution and will reject the excess carbon in the'form of carbides. Accordingly, it is essential to the formation of austenite and for the efficientutilization of the carbon present that the carbideseasily and quickly dissolve so that a completely austenitic structure may be attained in the least possible time and at the lowest possible temperature prior to quenching. Quenching times and temperatures that are excessive are uneconomical and may not be tolerated in the metals industry.

Quench-hardenable mild steels, which consist essentially of iron and carbon, in the annealed condition exhibit a spheroi'clized iron-carbon carbide generally regarded as being Fe C (cementite) which rapidly dissolve when the alloy is heated to a temperature above the transformation temperature of the specific steel to form austenite which then transforms to martensite upon quenching or quenching and tempering. In the case of quench-hardenable alloy steels, however, Where the alloys contain alloying metals which enter into the formation of complex metal carbides which do not readily dissolve to supply carbon for the purpose of obtaining an' austenitic structure, it is frequently necessary to heat the steels to temperatures far above the theoretical transformation temperatures and hold for much longer times to obtain adequate solution of the carbidesprior to quenching. For example, chromium will combine with iron and carbon to form a complex carbide regarded as 'M C (where M represents the metal constituents Cr and Fe in varying ratio and C represents carbon) which is considerably more sluggish in going into solution than Fe C. Molybdenum and/ or tungsten combine with iron'and carbon to form the 'complex carbide M C while vanadium combines to form the complex MC. The M C type carbide requires'exceedingly high temperatures (up to 2300 F.) before it will dissolve and the MC type carbides require such high temperatures and times to dissolve, it is not generally re- 3,150,444 Patented Sept. 29, 1964 garded as practical to attempt to take these carbides entirely into solution.

Since quench-hardenable alloy steels which contain alloying ingredients which form M C, Mg C and MC type carbides are relatively sluggish in their response to solution' heat treatment due to the presence of these complex carbides, it is preferable" that an annealed structure be obtained that exhibits a fine, even carbide distribution. The smaller and more evenly distributed carbides naturally dissolve more quickly and easily since they provide a greater surface area for dissolution and the matrix of the metal may absorb the carbon and alloy metal more evenly.

Present teeming and working techniques do not lend themselves tothe consistent production of a quench-hardenable steel that will have fine or small evenly distributed carbides in the annealed condition.

In the method of the present invention, it has been found that quench-hardenable alloy steels may be produced, which in the annealed condition Will exhibit M C, M C and MC type complex carbides in a consistently fine and evenly dispersed form so that such alloys will readily respond to quench hardening.

The method of the present invention is of particular significance when employed to produce high speed tool steels since these compositions contain relatively large amounts of the complex carbide-forming metals such as chromium, molybdenum, tungsten and vanadium. However, the present method may be employed advantageously in conjunction with any of the heat hardenable alloys in which the complex carbides of the M G, M C or MC type form a major portion of the carbides present in the annealed structure.

It is, accordingly, the object of the present invention to provide quench-hardenable alloy steels which, in the an nealed state, exhibit a uniform, evenly distributed, fine carbide structure;

It *is 'also an object ofthe present invention to i provide quench-hardenabl'e alloy steel which'm'ay be solution annealed at a minimum time and temperature prior to quenching.

A further object of the present invention is to provide a method of producing a quench-hardenable alloy steel that contains a fine, uniform dispersion of complex carbides of the M C, M gC or-MC type.

A still'further object of the present invention is to provide high speed'tool steels that exhibit a fine, evenly distributed carbide structure when in the annealed state that may be readily taken into solution when heat treated for quenching.

Other objects and advantageous features will be obvious from the following detaileddescription and drawings wherein:

FIGURE 1 is a photomicrograph taken at a magnification of 1500 diameters of a typical microstructure of an annealed, wrought, high speed tool steel (Mi-2); and

FIG. 2 is a photomicrograph taken at a magnification of 1500 diameters of the annealed microstructure of the same grade of'high speed tool steel as the material of FIG. 1 (M-2 tool steel), but manufactured by the method of the present invention.

In general, the present invention maybe said to be directed to a method whereby molten alloy steel of an analysis to effect a heat orquenchedhardenable composition which exhibits an annealed microstructure which contains one or more'of the complex carbides of the type M C, M C andrMC is atomized by a fluid stream and quenched by falling into a liquid medium, such powder is then compacted and sintered in the presence of a carbonaceous redu'c'ingatmosphere and then is mechanically worked until it possesses a density substantially equivalent to that of the same alloy in its normally wrought form. The steel is preferably atomized in such a manner as to create particles that are capable of passing through a 20 mesh screen, particularly where they are to be subsequently roll compacted into sheet or strip, but the particles may be as coarse as .25 inch in diameter where they are to be mechanically worked by forging or extrusion. The method of the present invention is particularly directed to quench-hardenable steels which contain as alloying ingredients at least one of the metals chromium, tungsten, molybdenum or vanadium in a total amount of at least about 1% up to about 40%, since such materials combine with carbon to produce the M C, M C and MC type complex carbides.

In the ordinary application of powdered metal, the powder itself may be obtained by a variety of methods including the reduction of oxides, milling, and atomization processes wherein a molten stream of metal is dispersed by a fluid stream. Ordinarily, however, the metal powders employed prior to sintering are unalloyed. In other words, mild steel particles or particles of iron are generally blended with powders of the alloying constituents prior to sintering in that it would not be economical to first produce the metal from the molten state as an alloy, then atomize it to effect a powder since once the alloying additions are made to the molten metal it is far more convenient to merely cast the molten metal into molds either to the shape desired or into ingots for subsequent fabrication.

Also, the compressed and sintered compacts are not ordinarily subsequently worked after they are formed or compressed so as to obtain a density equivalent to that of the wrought material, since it would be far more economical to obtain the wrought material by merely casting and working a prealloyed molten shape.

The prior art teaches some specific use of prealloyed powders; however, such compacted and sintered prealloyed powders are seldom converted into a wholly dense condition since such a conversion is economically unfeasible and generally there is no physical or mechanical advantage to such products over cast and wrought products. Also, the past ellorts in this direction have not been concerned with a hardenable material such as is the method of the present invention.

The present invention or method is applicable to any alloy steel that contains complex carbides of the M C, M C and MC type, but is particularly advantageous when employed in conjunction with high speed tool steels that nominally contain substantial amounts of alloying ingredients that are of a type or nature to combine with carbon to form such complex carbide systems.

In the complex carbides such as the M C type, tungsten and/or molybdenum plus iron is combined with carbon in a manner to effect such a carbide. The ratio of W and/or Mo to Fe may vary and the tendency of such carbides to go into solution may vary but the production of the carbide in a fine evenly dispersed state is beneficial regardless of such variations. The M C carbide as effected by the presence of chromium is considerably smaller than the M C type and consequently is not so easily observed. However, where the structure contains both M C and M C type carbides, both will be finer and more evenly dispersed when produced in accordance with the method of the present invention.

The MC type carbide caused by the presence of vanadium is not readily soluble whether large or small or whether or not it is evenly dispersed. Additions of vanadium to such compositions, however, are generally for the purpose of providing such carbides which contribute to the fine grain size of the alloy and provide abrasion resistance. Such properties are enhanced by the MC complex being present as a fine, evenly dispersed carbide so that the method of the present invention is equally applicable to the MC type carbide as well as the other mentioned carbide complexes.

Many alloys may contain some complex carbides of the M C, M C and MC type due to the presence of Cr, W, Mo and V in residualamounts. However, unless about 1%, by weight, of one of these materials is present, there is an insuflicient quantity of the complex carbides present to materially affect the response of these alloys to solution heat treatment.

The method of the present invention is particularly applicable to the hi h speed tool steels since these materials contain additions of all the alloying materials Cr, W, Mo and V and, consequently, exhibit a combined carbide structure of the M C, M C and MC types. These steels are particularly sluggish in their response to solution treatment and therefore show maximum beneficial response when produced by the method of the present invention. The high speed tool steels have the following approximate analyses:

Molybdenum Optional up to about 12%.

Quench-hardenable steel such as defined above, must, of course, contain carbon since it is the presence of carbon in iron which renders such steels hardenable. The quench-hardenable alloy grades normally contain about 1% of carbon, but may contain as little as .1% or as much as 3%, depending on the exact grade of steel involved.

Other alloying ingredients which do not enter into the carbide complex may be present. For example, manganese and silicon are usually present in some amount either as residual elements, necessary constituents for specific properties, or they may be added as scavengers and deoxidizers during melting procedures. Small amounts of nickel also may be present as a residual constituent or as a necessary component. Excessive amounts of nickel and manganese must, of course, be avoided to maintain the alloys as quench-hardenable grades. Up to 15% cobalt (as set forth above) may be present in high speed tool steels.

Other ingredients which may be present in quenchhardenable alloy steels, either as purposeful additions or as residual elements, include small amounts of Ti, Cb, Ta, Zr and Hf. These elements may participate in the forma tion of the complex carbides (M C, M C and MC) but are seldom employed in such amounts as to aiTect the solution treatment of quench-hardenable alloy steels.

Atomization of molten metals is a well-known method for obtaining metal powders and consists of pouring a molten stream through an area wherein it is impinged by a fluid which may be a liquid such as water or a gaseous substance such as steam, nitrogen, compressed air, etc., in a manner to disperse the falling metal into fine particles which then conventionally fall into a liquid medium, usually water, wherein they are quenched. Methods of atomization are old and well known in the prior art and by varying the intensity of the impinging fluid or gas and by employing a variety of nozzles to create such impinging sprays, the size and contour of the particles may be controlled. An adequate description of such apparatus and process is revealed in United States Patent No. 2,956, 304, William L. Batten et al. This patent reveals not only a suitable apparatus, but a suitable method of con trolling the size of the atomized particles. Although powdered metals may be manufactured by other means than the atomizing process, atomization is an essential step in the process of the present invention since it is the quench properties of the atomized particles that are. primarily responsible for the resultant highly desired fine, evenly dispersed, carbide structure. Hence, powdered metals manufactured by other means will not give the desired results, though compacted and sintered in accordance with the other steps of the present method.

By normal steel mill practice, high speed tool steel and hardenable grades of alloy steel, are produced by casting molten metal into ingots and processing these ingots into desired shapes through forging or press rolling techniques. Material produced in this manner has a fairly wide distribution of carbide sizes in the matrix metal. As the mechanism of the formation of non-uniform distributions of coarse and fine carbide sizes is not known, it has not been controlled to date.

It has also been observed that the carbide size distribution may vary from heat to heat, ingot to ingot, and, in many cases within an ingot. Such a variation leads to difiiculties in the heat treating of the material as the response to heat treatment is a function of the carbide size and distribution.

In the method of the present invention, it has been found that the alloy, as atomized, must have substantially the same composition as the wrought material desired, since in the atomizing process each particle has already been heat treated in a manner essential to the end results.

During the atomization process, an oxide film on the surface of the particles is inevitably formed. If the powder is heat treated in this condition a. reaction occurs between the carbon in. the powder and the oxide which results in a loss of carbon. A blend of lampblack and/or graphite and the metal powder is made, the lampblack and/or graphite serving as a reducing agent. The amount of lamp-black and/ or graphite. necessary will vary from lot to. lot of metal powder and may be determined experimentally. on small powder lots. By varying the percentage of lampblack or graphite in the metal powder and heating compacts of the blends at the anticipated processing temperature of the article for a given time, the required amount of lampblack may be determined by the carbon content of the compact. However, it will be appreciated that any specific addition of carbon will enhance the resultant material by reducing the carbon loss through reducing the oxides present. Amounts oflarnpblack and/ or graphite as small as .l%, by weight, of the blended powders, has been found to significantly deter decarburization while amounts exceeding about of the weight of the powder effects a blend that may be too fragile (lacks sufiicient green strength) for handling after compacting. Consequently, it may be said that for practical applications, the carbon and/or lampblack content should be at a level of from about .1% to 5%, by weight, of the total blended powders.

The metal powder itself need only be fine enough to be compacted. Where mechanical working is to be accomplished by means of rolling into strip or sheet, the particle size may be as coarse as that which will pass through a 20 mesh screen (840 micron opening) but preferably should be of a size that will pass through a 100 mesh screen (a 149 micron opening). If the particles exceed in size those that will pass through a 20 mesh screen, they will resist roll compacting and upon subsequent mechanical deformation may fail to obtain substantially equivalent density to the wrought material. When the material is to be forged or extruded, the metal particles may be much larger (up to %-lI1Ch diameter), although finer particles (which will pass through a 20 mesh screen) are preferred.

The particle size of the lampblack and/or graphite is not critical since these materials, intheir ordinarily available commercial; state, possess a particle. size that will ordinarily pass through a 325 mesh screen. It may be stated, however, that these materials preferably should be. no coarser than a particle size that will pass through a 100 mesh screen.

As an alternate method of providing a carbonaceous atmosphere one may supply a carbonaceous gaseous material such as a hydrocarbon gas during sintering. Such gas may be methane, propane or any of the hydrocarbon gases which do not contain interfering constituents such as oxygen. Should such a gaseous substance be employed, it is preferable that it constitute at least0.1% volume of the total atmosphere, the balance preferably being a reducing atmosphere, such as hydrogen.

The atmosphere used in conjunction with the solid carbonaceous material, i.e. lampblack and/ or graphite, should be a non-oxidizing atmosphere, preferably a reducing atmosphere. The presence of a reducing atmosphere, such as hydrogen, assists in reducing the oxide coating always found on atomized steel particles. A hydrocarbon gas, such as methane, is reducing in itself although it"also is preferably used in conjunction with a reducing gas, such as hydrogen. 7

It is desirable and preferable that all the particulate material be dry and that the moisture content of the reducing atmosphere also be kept low (preferably a dew point of about -40 F. or lower).

The exact method of compacting is, of course, determined by the shape of the object desired, to some extent. Of course, strip, bars, billets, wire, etc., may be fabricated from the compressed and sintered compacts in the manner of ordinary cast and wrought metals. However, it may be expedient, particularly where making a flat rolled product such as strip or sheet, to compact the metal between rolls in the method generally employed to effect such. a strip product. Methods of accomplishing this are taught in United States Patents Nos. 2,582,744, I. B. Brennan, 2,937,942,.F. L. Lenel, 2,935,402, F. J. Trotter et al'., 2,758,336, H. Franson and 2,746,741, G. Naeser. For example, we have had particular success inproducing high speed tool steel for band. saw blades from AISI M-Z analysis by compacting powders in strip form, sintering in a carbonaceous atmosphere and cold rolling to effect a density substantially equivalent to the rolled M-2 composition.

After compacting andsintering, the material processed in accordance with-the method of the present invention is mechanically worked until, it has reached a density approximately equivalent to that it possesses in the cast and wrought state. Preferably an equivalent density is reached because any porosity; remaininglowers the strength properties' below that of the conventionally produced materials However, for some applications some reductions in strength properties may be tolerated'so that a density of at least 9 0% ofthatattained by the ordinary cast and wroughtmaterial may be regarded as a minimumacceptable density. Mechanical working may be hot or cold so long as the required density is attained. For'example, in the roll compacting of M2'high speed. tool steel strip, the compacted and sinteredstrip isalternately cold rolled. and annealed until the desired density is reached. However, when extruding, it may be desirable toextrude the material while hot.-

The advantages of the method of'the present invention are particularly apparent from the :FIGURES 1 and 2. FIG. 1 shows the structure ordinarilyobtained by teeming ingots of M-2 high speed tool steel; which nominally has an analysis of 0.80% carbon, 4% chromium, 2% vanadium, 6 4% tungsten, 5.00%. molybdenum. and the balance iron. FIGS.. 1': and 2 are photomicrographs of specimens of M-2 tool steel that were etched .bydipping the specimens, intoltan aqueous solution; of 4% sodium hydroxide saturated with potassium: permanganate for about 5 seconds. The M C type:carbides are identified in FIG. 1 as 11 and the MC carbides as 12. The M 0 carbides are not visible though their presence is known. No attempt has been. made to identify the carbides of FIG. )2 since they are so fine it isnot' possible to clearly differentiate between 'them. The. specimen of FIG. 1 was taken from M-2 tool steel which was cast,

forged and annealed in the conventional manner while the specimen of FIG. 2 was taken from strip material processed as set forth below as an example of the method of the present invention. The timer carbide structure shown by FIG. 2 is readily observable.

The following is a general outline of the present method as applied to the production of AISI M2 tool steel strip for band saw blade application:

(1) Lampblack and metal powder are blended.

(2) The blend is heat treated to anneal the powder. The powder is extremely hard due to the water atomization treatment and must be annealed to become plastic.

(3) The powder is roll-compacted into continuous lengths. The width and thickness of the strip are governed by the physical size of the compacting mill. The length of the strip is governed by the handling facilities adjacent to the compacting mill.

(4) The compacted powder is treated in dry hydrogen at a temperature of 2000 F. to 2150 F. for a time necessary to cause sintering. Generally, the longer the time and higher the temperature, the higher the density of the sintered strip. The strip is cooled at a rate to allow annealing.

(5) The strip is cold rolled without liquid lubricant to a thickness governed by the edge cracking of the strip. When edge cracking appears, cold rolling is discontinued. A lubricant is not used as it enters the pores of the sintered strip and becomes entrapped.

(6) The strip is reheated at a temperature of 2000 F. to 2150 F. for a time necessary to cause further densification. The annealing cycle follows this treatment.

(7) The strip is further cold rolled and annealed until the desired thickness is achieved.

The following are specific examples of the method of the present invention and are given to illustrate the present method but in no way limit the claims to the exact embodiments set forth.

A lot of M-2 prealloyed high speed tool steel having a ladle analysis as follows:

was converted into strip material in the following manner: 1.04 percent by weight, lampblack was blended with the metal powder. The blend was annealed in a dry hydrogen atmosphere at 1600 F. for 2 hours, cooled to 1400 F., held 6 hours and furnace cooled to room temperature. The powder was then roll-compacted, by being projected from a hopper from above a set of polished rolls, into strips approximately 0.070 thick x 1% wide x 18" long. The strips were then processed as follows:

(1) Sintered for 30 minutes at 2150 F. in dry hydrogen, furnace cooled in dry hydrogen to 1400 F., held six hours, furnace cooled to room temperature in dry hydrogen.

(2) Cold rolled 33% from 0.060" to 0.040" to a density of 5.42 gm./cu.cm.

(3) Repeat sintering treatment (1).

(4) Cold rolled 18.8% from 0.040" to 0.0325 to a density of 7.69 gm./cu.cm.

(5) Repeat sintering treatment (1).

(6) Cold rolled 13.8% from 0.0325 to 0.028 to density of 8.02 gm./cu.cm.

(7) Heat treated 60 minutes at 1650 F., cooled 50 F./hour to 1200" F., furnace cooled in hydrogen.

(8) Cold rolled 46.4% from 0.028" to 0.015" to a density of 8.15 gm./cu.cm.

(9) Repeat step (7) as a final annealing cycle.

The above treatment produced solid strips of high speed tool steel 0.015" thick X 1%" wide x 10 to 2 long having a density equal to that published for conventional produced material. (8.15 gms./cu.cm.).

The structure of FIG. 2 is that of the annealed strips produced as above.

M2 tool steel atomized powders which have been produced by teeming molten tool steel while impinging the metal stream with water to effect a breaking up of the particles into sizes all of which were capable of passing through a .2 0 mesh screen and which particles were quenched in water after atomization were found to have the following approximate analysis:

Si Mn S P Cr M0 These powders were annealed for approximately one hour at 1625 F., cooled to 1400 F., held six hours and furnace cooled to room temperature in dry hydrogen.

The powder was then divided into three lots and processed individually as follows:

(1) Lampblack additiom-Previously dried lampblack of 325 mesh size was intimately blended with the metal powder in the weight percentages listed below. -Fivegram samples of each blend were compacted in a /z-inch diameter die at 25 tons per square inch. These were sintered in hydrogen for one (1) hour at 2150 F., cooled to 1400 F., held six (6) hours, and furnace cooled. The compacts were then analyzed for weight percent of carbon. Results are as follows:

Wt. Percent Weight Percent Lampblack of Carbon in Blended Sintered Compact Wt. Percent Weight Percent Graphite of Carbon in Blended Sintered Compact (3) Hydrocarbon atm0sphere.-Ten grams of the annealed powder were compacted at 40 t.s.i. without any carbon additions. The compacts were sintered for one hour at 2000 F. in dry hydrogen to which small volume percentages of methane were added. The compacts were cooled at an unknown rate. The carbon content 9 of each compact was determined with results indicated below:

Volume Percent Weight Percent of Methane in of Carbon-in Dry Hydrogen SinteredCompact The variation in sintering temperature among the three conditions of either 2000" F. or 2150 F. is not considered important .as both temperatures are adequate for sintering. Compacts made by all three of the methods above were mechanically worked as by forging to obtain a density approximately equivalent to that of cast or wrought M-2 tool steel (about 8 to 8.25 grams per cubic centimeter.) Microstructuresof .all three exhibited a structure similar to that .of FIG. 2.

As additional examples .of the method of the present invention, molten vanadium alloy high speed tool steel was atomized, by impinging a molten stream of said metal with water spray and collectingthe atomized powder in a water tank. This material was ,AISI Type T- tool steel and the prealloyed atomized powder had the following analysis:

C M11 P 8 S1 C1 Mo W V Co The prealloyed powders were then processed into a compact of a density substantially equivalent to the wrought alloy in the following four steps:

Step 1: -100 mesh powder was annealed for one hour at 1650 F., furnace cooled to 1400* F., held six hours, furnace cooled to room temperature in pure dry hydrogen atmosphere.

Step 2: gram samples were compacted in a /2-inch diameter die at tons/ square inch.

Step 3: One compact was sintered at 2000 F. for one hour in each of the atmospheres listed below. The carbon content of each compact was determined with the following results:

Step 4: As 0.81% is within the desired range for the AISI Type T-5 composition (0.80% C typical), the compact was treated as follows to obtain near theoretical density:

(a) Coined in /2 -inch diameter die at t.s.i.

(b) Annealed /2 hour at 1600 F., furnace cooled to 1400 F., held six hours, furnace cooled to room temperature in pure dry hydrogen.

(0) Step (a) repeated.

(d) Step (b) repeated.

As a still further illustration of the method of the present invention atomized prealloyed powder of AISI Type 430 stainless steel was compacted and converted to AISI Type 4400 stainless steel (a high chromium hardenable grade of stainless steel) as follows:

0 M11 P S Si Step 1: 10 gram samples of the as atomized powder were compacted in a /2-inch diameter die at 20 tons/ square inch.

Step 2 One compact was sintered at 2000 F. for one .hour in each of the atmospheres listed below. The carbon content of each compact was determined with the following results:

Step 3: As 0.98% carbon is within the desired range for the AISI Type 440C composition (0.951.20% C), the compact was treated as follows to obtain near theoretical density:

(a) Coined in /z-inch diameter die at 25 t.s.i.

(b) Annealed /2 hour at 1600" F., furnace cooled to 1.400" F., held six hours, furnace cooled to room temperaturo in pure dry hydrogen.

(0) Stop (a) repeated.

(d) Step (b) repeated.

I claim:

1. The method of producing a heat hardenable alloy steel .the composition of which includes at least 1% of at least one of the elements of the group consisting of chromium, vanadium, molybdenum and tungsten, said alloy steel being characterized by an annealed structure which consists essentially of fine, evenly distributed carbides of at least one of the types M C, M C and MC in a ferritic matrix which comprises, compressing atomized prealloyed powder of said steel, said powder having a particle size of up to .25" diameter, sintering said compacted powder in the presence of a carbonaceous reducing atmosphere and mechanically working said compacted and sintered powder so as to effect a density substantilaly equivalent to said steel in its cast and wrought state.

2. The method of producing a heat hardenable alloy steel the composition of which includes at least 1% of at least one of the elements of the group consisting of chromium, vanadium, molybdenum and tungsten, said alloy steel being characterized by an annealed structure which consists essentially of fine, evenly distributed carbides of at least one of the types M C, M 0 and MC in a ferritic matrix which comprises, compressing atomized prealloyed powder of said steel, said powder having a particle size sufliciently fine to pass through a 20 mesh screen, sintering said compacted powder in the presence of a carbonaceous reducing atmosphere and mechanically working said compacted and sintered powder so as to effect a density substantially equivalent to said steel in its cast and wrought state.

3. The method of claim 2 wherein said prealloyed powder is blended with at least one material selected from the group consisting of lampblack and graphite prior to sintering.

4. The method of producing a heat hardenable alloy steel the composition of which falls within the following analysis ranges:

Carbon About .6 to 2.5%.

Silicon About 1% max. Manganese About 1% max.

Sulfur About 04% max. Phosphorus About .04% max. Chromium About 2 to 9%. Vanadium About .5 to 7%.

Cobalt Optional up to about 15%. Tungsten Optional up to about 24%. Molybdenum Optional up to about 12%.

the composition of which includes at least 1% of at least one of the elements of the group consisting of chromium, vanadium, molybdenum and tungsten, said alloy steel being characterized by an annealed structure of fine, evenly distributed complex carbides in a ferritic matrix which comprises, atomizing molten steel of said composition to obtain a powder sufficiently fine to pass through a 20 mesh screen, compacting said powder and sintering said .5 compacted powder in the presence of a carbonaceous reducing atmosphere and mechanically working said compacted and sintered powder so as to eifect a density substantially equivalent to said steel in its cast and wrought state.

5. The method of producing a heat hardenable alloy steel the composition of which falls within the following analysis ranges:

Carbon About .6 to 2.5%.

Silicon About 1% max. 15 Manganese About 1% max.

Sulfur About .05 to .5 max. Phosphorus About 04% max. Chromium About 2 to 9%.

Vanadium About .5 to 7%. Cobalt Optional up to about 15%. Tungsten Optional up to about 24% Molybdenum Optional up to about 12%.

the composition of which includes at least 1% of at least 25 one of the elements of the group consisting of chromium, vanadium, molybdenum and tungsten, said alloy steel being characterized by an annealed structure of fine, evenly distributed complex carbides in a ferritic matrix which comprises, atomizing molten steel of said composition to obtain a powder sufficiently fine to pass through a 20 mesh screen, compacting said powder and sintering said compacted powder in the presence of a carbonaceous reducing atmosphere and mechanically working said compacted and sintered powder so as to effect a density substantially equivalent to said steel in its cast and wrought state.

6. The method of claim 5 wherein said powder is blended with at least one material selected from the group consisting of lampblack and graphite prior to sintering.

References Cited in the file of this patent UNITED STATES PATENTS 2,746,741 Naeser May 22, 1956 2,757,446 Boegehold et al. Aug. 7, 1956 2,828,202 Goetzel et al. Mar. 25, 1958 2,956,304 Batten et al. Oct. 18, 1960 3,053,706 Gregory et al. Sept. 11, 1962 OTHER REFERENCES Precision Metal Molding, A New Prealloyed Stainless Steel Powder, 5 pp., May 1954. 

1. THE METHOD OF PRODUCING A HEAT HARDENABLE ALLOY STEEL THE COMPOSITION OF WHICH INCLUDES AT LEAST 1% OF AT LEAST ONE OF THE ELEMENTS OF THE GROUP CONSISTING OF CHROMIUM, VANADIUM, MOLYBDENUM AND TUNGSTEN, SAID ALLOY STEEL BEING CHARACTERIZED BY AN ANNEALED STRUCTURE WHICH CONSISTS ESSENTIALLY OF FINE, EVENLY DISTRIBUTED CARBIDES OF AT LEAST ONE OF THE TYPES M6C,L M23C6 AND MC IN A FERRITIC MATRIX WHICH COMPRISES, COMPRESSING ATOMIZED PREALLOYED POWDER OF SAID STEEL, SAID POWDER HAVING A PARTICLE SIZE OF UP TO .25" DIAMETER, SINTERING SAID COMPACTED POWDER IN THE PRESENCE OF A CARBONACEOUS REDUCING ATMOSPHERE AND MECHANICALLY WORKING SAID COMPACTED AND SINTERED POWDER SO AS TO EFFECT A DENSITY SUBSTANTIALLY EQUIVALENT TO SAID STEEL IN ITS CAST AND WROUGHT STATE. 